In optical networks, optical control (e.g., for power, Optical Signal-to-Noise Ratio (OSNR), etc.) is generally performed on a section in the optical network. A section is an optical link with no optical add/drop between two nodes, i.e., the section is defined between optical add/drop points. Thus, the optical link in the section has the same number of channels at ingress and egress, which is advantageous for sectional control via a sectional controller. In the overall network, control is performed through various techniques known in the art for each section. See, e.g., U.S. Pat. No. 9,577,763, issued Feb. 21, 2017, and entitled “SPECTRUM CONTROLLER SYSTEMS AND METHODS IN OPTICAL NETWORKS,” the contents of which are incorporated by reference herein. Sectional optical controllers run with a fundamental assumption that the spectral loading within the section remains unchanged and based on that, the sectional controllers run all their optimization applications such as optimizing power or incremental OSNR. One particular constraint in conventional section control-based schemes is the assumption the sectional controller has visibility of the optical components, to be able to determine where the sections are. Of course, this is the case in a single vendor deployment. However, this is not the case with submarine systems, third-party optical networks, and the like. In such other deployments, sectional control is difficult or impossible to implement since the sectional controller simply does not have visibility of the underlying optical components and does not know how many sections there are between two add/drop nodes.
For example, in a subsea (also known as a submarine) optical network, the optical components under the sea are typically left as self-controlled. That is, the long chain of optical amplifiers run control operations (typically total optical output power or constant pump current controlled) on their own. The Reconfigurable Optical Add/Drop Multiplexers (ROADMs) are typically located at the landing stations at the two ends of the submarine cable and provide the optical channel add/drop functions and further branching to remote terrestrial networks. The ROADM terminals at the two ends of the submarine cable typically do not maintain any direct control communication with the long chain of optical amplifiers that is primarily due to the unavailability of any Optical Service communication Channel (OSC) between the ROAMs and the subsea-amplifiers, and due to the fact, that often service providers deploy ROADM terminals and subsea-amplifiers from different optical vendors who do not communicate in the same format, nor in the same communication channel.
In a typical submarine network, submarine cables with a long-chain of amplifiers usually run unprotected. This is usually due to the fact that submarine cables, as laid down under the sea, do not see the usual fiber cut disturbance as a typical terrestrial optical fiber cable would see. However, if for any reason, a subsea fiber cut takes place, the communication disruption becomes enormous, and typically, it takes weeks to months to repair such fiber faults. In order to overcome such expensive traffic disruption, in some submarine networks, service providers are planning to place optical Branching Units (BUs) under the sea so that if a fiber cut takes place within a portion of a protected submarine cable, then traffic can be automatically re-routed using the optical branching unit to other subsea cable routes.
There are various challenges associated with interoperation between the ROADMs and the submarine optical system. Also, these same challenges are seen in the case of ROADMs operating on third-party optical networks, i.e., third-party optical components including OADMs between the two ROADMs. A first challenge is how the ROADM terminals located at the edge of submarine cables (or third-party optical network) can detect any fiber break, or foreign equipment failure within the foreign-controlled submarine territory (or third-party optical network), and in the absence of any optical supervisory communication channel. Note, in this case, the submarine links add a discrete challenge for not creating a loss of light indication at the receiving end of the subsea link due to the presence of high Amplified Stimulated Emission (ASE). A second challenge is how the Layer 0 control plane that is responsible for maintaining the routing and end-to-end channel topology, can detect the automatic reconfiguration of channels from the faulted cable to one of the other non-faulted branching paths as maintained and controlled by the foreign reconfigurable/fixed optical branching units, and again with or without any per channel reconfiguration notifications from the foreign BUs to the ROADM terminals.
A third challenge, based on the first and second challenges, is how the Layer 0 control plane can reroute any “mesh restorable” channels from the faulted cable to another restoration path (since it is possible that not every channel on the faulted path may not have the policy to be mesh-restorable), where the re-routing scheme involves clearing channel topology from the faulted cable, re-creating end-to-end channel topology between source and destination points over the other possible restoration paths in the network, including the under-the-sea branching path, where the channel is automatically re-routed by the foreign BUs, and if necessary, retuning the channel at a different frequency in case there is a spectrally flexible reconfigurable subsea BUs.
As sectional controllers are well known and work effectively, there is a desire to extend their benefits to optical links which are not necessary well-defined sections. Specifically, the connectivity between the ROADMs described above over the submarine optical network or the third-party optical network is not a defined section with the presence of BUs or OADMs and without visibility by the ROADMs, and it would be advantageous to extend the benefit of sectional control thereto.